Set pull policy to always for chatops commands

What does this MR do and why?

We noticed that the build:image job was running and successfully pushing a new :latest image to the ops instance, but when running chatops commands, the changes were not showing. We verified the image was building correctly and pushing, so we determined it must have to do with the pull aspect for the job.

From slack:

from the chatops jobs

Using Kubernetes namespace: gitlab-runner
Using Kubernetes executor with image registry.ops.gitlab.net/gitlab-com/chatops:latest ...
Using attach strategy to execute scripts...

Now that we are using runners in Kubernetes for ops.gitlab.net, the default imagePullPolicy is ifNotPresent so using tags which change (like latest ) is going to give unpredictable results

This can be fixed by setting the pull policy for the image to always, which is what we do in this MR.